1. Field of the Invention
The present invention relates to a fixing device including a peeler and an image forming apparatus including the fixing device.
2. Description of the Background Art
An image forming apparatus for forming a toner image with toner includes a fixing device configured to fix the toner image on a sheet or similar recording medium. The fixing device includes a heat roller accommodating heating means therein and a press roller pressed against the heat roller. The heat roller and press roller fix a toner image carried on a sheet with heat and pressure while nipping the sheet therebetween. To reduce toner offset, the surface of the heat roller is coated with Teflon (trade name) or covered with a Teflon tube that enhances parting ability. Further, a peeler is held in contact with the heat roller for preventing the sheet from wrapping around the heat roller due to, e.g., toner adhered to the heat roller. The peeler is positioned slightly above the nip between the heat roller and the press roller. In this condition, the underside of the peeler serves to guide the sheet between the heat roller and an outlet roller pair.
The fixing device described above has the following problem left unsolved. When the sheet jams a path preceding the outlet roller pair, it deforms in the form of bellows and contacts the edge portion of the peeler. As a result, the sheet presses the peeler in the direction in which the peeler bites into the heat roller. This causes the peeler to peel off the Teflon layer of the heat roller or otherwise damage it and makes it necessary to replace the heat roller.
To solve the above problem, Japanese Patent is Laid-Open Publication No. 2001-240284, for example, proposes a fixing device including a peeler configured such that when a jamming sheet presses the edge of the peeler, a support shaft supporting the peeler moves in the direction in which the peeler does not bite into a heat roller. Even such a fixing device has a drawback that when the sheet presses the peeler more than expected, the peeler scratches the heat roller with its edge. Particularly, as for a heat roller covered with an elastic layer for enhancing image quality, the peeler bites into the elastic layer more than into the Teflon layer even if the pressing force is weak.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Publication No. 8-29873 (Japanese Patent Laid-Open Publication No. 61-86343) and Japanese Patent Laid-Open Publication Nos. 10-74015, 2002-14565 and 2002-145503.
It is an object of the present invention to provide a fixing device capable of protecting a rotary body from damage even when a peeler is pressed against the rotary body more than expected, and an image forming apparatus using the same.
A fixing device of the present invention includes a rotary body and a peeler rotatable about a support shaft and including an edge portion capable of contacting the surface of the rotary body. The edge portion includes a guide surface opposite to a surface that faces the rotary body. A first biasing device exerts on the peeler a force that tends to cause the edge portion to contact the rotary body about the support shaft. A guide guides the support shaft between a contact position where the edge portion contacts the rotary body and a non-contact position where the former is released from the latter. A second biasing device biases the support shaft toward the contact position. A guide member includes a guide surface that becomes substantially flush with the guide surface of the edge portion when the peeler is moved from the contact position toward the non-contact position against the action of the second biasing means.